1. Field of the Invention
The present invention relates to a heater apparatus that may be attached to a water tank, for example an aquarium or to a vessel for containing liquid, the heater apparatus being arranged so as to keep constant the temperature of water or liquid held inside the tank or vessel.
2. Description of the Related Art
There exist heater apparatuses which have their heating elements attached to an aquarium or to a like vessel in order to heat water inside the tank. This type of heater apparatus includes a temperature sensor that is generally submerged in water inside the tank. In accordance with detected temperatures from the temperature sensor, the heater apparatus controls its heating elements in operation so as to keep constant the water temperature in the water tank.
The temperature sensor is placed, often sheathed, inside the water tank or vessel. In such a state, the sensor comes into contact with what is contained in the water tank or vessel. This raises a possibility that the temperature sensor can be damaged by the contents of the tank. Because impurities can stick to the temperature sensor, users are required to clean and maintain them frequently to ensure accurate temperature control.
The heating elements under control are generally switched on and off depending on the temperature of that which is contained in the water tank or vessel. However, it is the heating elements that are controlled, not the heating itself in a meticulous fashion. As long as there is a sufficient quantity of what is contained in the water tank or vessel, heating control is accurate. But if there is an inordinately reduced quantity of contents or nothing left of the contents inside because of leakage and evaporation, heating cannot be controlled precisely. With little or no liquid in the water tank or vessel, the temperature sensor will detect ambient air temperature. If the detected temperature is lower than a set temperature, the heater apparatus will keep operating its heating elements. Anything that surrounds the heating elements can then be overheated leading to a hazardous situation.
Thermal fuses or thermostats are generally used to prevent heating elements from overheating. However, these protective devices can act only a limited number of times where they are installed. Besides, they add costly chores of inspection and maintenance to users'responsibilities.